One-Stage Synthesis of Triptane-Enriched Gasoline by CO2 Hydrogenation

Abstract

In the presence of bifunctional combined catalysts, including oxide CuZnAl/Al₂O₃ and zeolite Pd-La_t/pHY/Al₂O₃ catalysts, a one-stage synthesis of liquid hydrocarbons was carried out from CO₂ and H₂ under conditions that were rather severe for the synthesis of triptane (340 °C, 10 MPa, GHSV = 20 000 h^–1). It was shown that for the combined catalyst, the most optimal ratio of CuZnAl–Al₂O₃ and Pd-La_t/pHY/Al₂O₃ catalysts is their ratio in the form of a physical mixture equal to 2:1. The introduction of La into HY via one-stage ion exchange in an autoclave at an elevated temperature and pressure (185 °C, 2 MPa) ensured a uniform distribution of lanthanum cations in the zeolite crystal volume, positively affecting gasoline selectivity. On CuZnAl/Al₂O₃ + Pd-La_t/pHY/Al₂O₃ combined catalyst, a selectivity for gasoline of 35 wt % (56 wt % based on the total amount of hydrocarbons) with an isoalkanes content of 80 wt %, including 12 wt % triptane, was achieved. CO₂ conversion (28%) and C₅₊ selectivity remained stable for 72 h. The work demonstrates the practical possibility of obtaining triptane-enriched gasoline via one-stage synthesis from CO₂ and H₂, which by its composition is the basic component of environmentally friendly motor fuels.